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Blood Introduction
Blood is a mixture of two things: cells and plasma. The heart pumps blood through the arteries, capillaries and veins to provide oxygen and nutrients to every cell of the body. The blood also carries away waste products.
The adult human body contains approximately 5 liters (5.3 quarts) of blood; it makes up 7 to 8 percent of a person's body weight. Approximately 2.75 to 3 liters of blood is plasma and the rest is the cellular portion.
Plasma is the liquid portion of the blood. Blood cells like red blood cells float in the plasma. Also dissolved in plasma are electrolytes, nutrients and vitamins (absorbed from the intestines or produced by the body), hormones, clotting factors, and proteins such as albumin and immunoglobulins (antibodies to fight infection). Plasma distributes the substances it contains as it circulates throughout the body.
Red Blood Cells
Red blood cells (RBCs), also known as erythrocytes, are by far the most abundant cells in the blood. RBCs give blood its characteristic red color. In men, there are an average of 5,200,000 RBCs per cubic millimeter (microliter), and in women there are an average of 4,600,000 RBCs per cubic millimeter. RBCs account for approximately 40 to 45 percent of the blood. This percentage of blood made up of RBCs is a frequently measured number and is called the hematocrit. The ratio of cells in normal blood is 600 RBCs for each white blood cell and 40 platelets.
There are several things about RBCs that make them unusual:
An RBC has a strange shape -- a biconcave disc that is round and flat, sort of like a shallow bowl.
An RBC has no nucleus. The nucleus is extruded from the cell as it matures.
An RBC can change shape to an amazing extent, without breaking, as it squeezes single file through the capillaries. (Capillaries are minute blood vessels through which oxygen, nutrients and waste products are exchanged throughout the body.)
An RBC contains hemoglobin, a molecule specially designed to hold oxygen and carry it to cells that need it.
The cellular portion of blood contains red blood cells (RBCs), white blood cells (WBCs) and platelets. The RBCs carry oxygen from the lungs; the WBCs help to fight infection; and platelets are parts of cells that the body uses for clotting.
The primary function of red blood cells is to transport oxygen from the lungs to the cells of the body. RBCs contain a protein called hemoglobin that actually carries the oxygen. In the capillaries, the oxygen is released to be used by the cells of the body. Ninety-seven percent of the oxygen that is carried by the blood from the lungs is carried by hemoglobin; the other three percent is dissolved in the plasma. Hemoglobin allows the blood to transport 30 to 100 times more oxygen than could be dissolved in the plasma alone.
Platelets
Platelets
The purpose of platelets
Platelets are the cells that circulate within our blood and bind together when they recognize damaged blood vessels. When you get a cut, the platelets bind to the site of the damaged vessel, thereby causing a blood clot. The evolutionary reason why they are there is to stop us from bleeding.
What makes platelets change their shape?
Platelets, the smallest of our blood cells, can only be seen under a microscope. They are shaped like small plates in their non-active form. A blood vessel will send out a signal when it becomes damaged. When platelets receive that signal, they will respond by traveling to the area and forming a clot. To make contact with the broken blood vessel, platelets grow long tentacles and then resemble a spider or an octopus.
What is a healthy platelet count?
A normal platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. Having more than 450,000 platelets is a condition called thrombocytosis; having less than 150,000 is known as thrombocytopenia. You get your platelet number from a routine blood test called a complete blood count (CBC).
What it means to have too many platelets (thrombocytosis)
The medical term for having too many platelets is thrombocytosis, and there are two types:
Primary or essential thrombocytosis: Abnormal cells in the bone marrow cause an increase in platelets, but the reason is unknown.
Secondary thrombocytosis: The same condition as primary thrombocytosis, but may be caused by an ongoing condition or disease such as anemia, cancer, inflammation, or infection.
White Blood Cells
White Blood Cells
White blood cells protect your body against infection. As your white blood cells travel through your bloodstream and tissues, they locate the site of an infection and act as an army general to notify other white blood cells of their location to help defend your body from an attack of an unknown organism. Once your white blood cell army arrives, they fight the invader by producing antibody proteins to attach to the organism and destroy it.
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